Cylindrical containers intended for retaining chemicals, industrial materials, and the like, when configured in larger, drum sizes generally are structured either of a metal such as steel or, particularly in North America, of a fiber material. Such fiber drums are formed having a metal chime and a replaceable lid which typically is retained in position by a split ring clamp. Other regions of the globe, particularly Europe and the Far East, form such non-metallic varieties of drums of a plastic rather than fibrous material. With the rapid globalization of commerce, a trend toward a somewhat universal use of plastic material for fabricating drums and associated lids has been observed. In this regard, there are ecological advantages associated with such uses of plastic, the material forming the drums and lids, for the most part, being recoverable. International standards also are developing which may supplant national standards for the performance of these drums. In this regard, standards have been promulgated by the United Nations organization. Department of Transportation Standards typically called for a 45.degree. inverted drop test from a height of 4 feet wherein the drums are filled with dry, finely powdered material to an authorized net weight in a lid. Depending upon the U.N. standards involved, the containers then are called upon to withstand a 45.degree. inverted drop from varying heights onto a hard surface such as concrete. The varying heights of 2 feet, 4 feet, and 6 feet are classified as X, Y, and Z. Classification of the proper designation for a container, which appears on the drum, for example Y-150 indicates that the container passes a 4 feet inverted drop with 150 Kg of dry product. To pass such tests or standards, the drum and lid combinations must recover from such drops without rupture or leakage. One international test approach involves a similar drop test except that the drums are filled with water instead of powdered materials. Such tests also include a seal test wherein the drums are filled with water, laid on their sides on a horizontal surface to determine the presence of leakage. Another test for leakage is the tip over test. In this test, a drum filled with water with lid and lockband properly installed is placed on a shipping pallet having a height of 4 inches. The conntainer is then pushed over allowing the container to fall on its side. In this test, no seepage of water is to occur.
Lids typically enclosing the drums are formed as stamped metal, fiber or plastic components which are secured over the rim-chime assemblies with metal split ring clamps having a channel or U-shaped cross section, the lower inwardly turned side or edge of which engages a rim or groove of the lid-drum interface and the upper side of which abuts over the lid top. An over-center lever generally is used to draw the ends of the split ring clamp structure together. For many packaging, transportation, and incinerator container applications, industrial users of such structures have sought to avoid metal components such as lids and lid retainers including the split ring clamping device. These metal devices do not burn, are prone to corrode, or, importantly, to insert minute metallic contaminants with the material packaged within the containers. Plastic lids have been successfully developed, for example as described in U.S. Pat. No. 4,718,571, by Bordner and for some period of time, the development of corresponding plastic clamping rings which remain competitive in terms of cost and securement performance was an elusive objective for investigators, until Bordner, et al., evolved a successful all plastic polymeric two-piece split ring clamp. This clamp, which found success in conjunction with fiber type drums, is described in U.S. Pat. No. 5,129,537, issued Jul. 14, 1992, and entitled "Two-Piece Polymeric Lid Clamping Ring".
The plastic lids and split ring clamps heretofore developed have performed quite well in combination with inherently rigid fiber drums. However, their experimental application to plastic drums has demonstrated a need for greater strength. An improved, two piece polymeric split ring clamp suited for use with the all plastic container combination is described in co-pending application for United States patent entitled "Polyermic Split Ring Clamp" by Bordner, et al., filed May 2, 1996 Ser. No. 08/643,249 (now U.S. Pat. No. 5,713,482, issued Feb. 3, 1998).
Another important aspect of the all plastic container systems resides in their reusability. Inasmuch as the drums are formed entirely of polymeric material, they may be cleaned and reused to achieve a substantial financial savings. However, this economically desirable reusability feature has not been available in the case of lids. To be practically cleanable utilizing automated scrubbing systems, crevices or like geometric configurations which would require manual cleaning procedures should be avoided. Otherwise, the cleaning cost renders the reuse feature unfeasible. Another block to lid reusability or reconditioning has been associated with the removal of the polymeric gasket functioning as a seal between the lid and an associated drum. Traditionally, this gasket has been formed of polyurethane which is fabricated in situ within the lid rim structure. Because of its adherence to the lid, the removal of such gaskets as a part of a cleaning process has been impractical to further defeat the otherwise desirable attainment of a reusable lid.
In 1996, Bordner, et al. introduced a molded plastic lid which achieved an enhanced strength in combination with improved cleanability by utilizing a structure wherein the central or intermediate region of the lid is configured as a sequence of waves which extend with gradually increasing amplitude from the lid center to a peripheral ring band. That ring band nests against the inside wall of the top portion of an associated drum when the lid is installed. Additionally, the structural integrity of this lid is enhanced by the fashioning of its center portion in a manner wherein the wave crest edges define a shallow dome. The smoothly transitioning crest-trough geometry promotes cleanability and thus, its practical reusability. To complement this cleanability feature of the configuration of the lid, its rim structure is fashioned in concert with a removably installed polymeric gasket. The gasket is provided having a ring seal portion which is removably insertable within a sealing cavity located at the rim of the lid. This ring seal may be extruded with a thermoplastic rubber exterior skin and an internally disposed foamaceous material. The waveform lid is described by Bordner, et al., in application for United States patent Ser. No. 08/643,236, entitled "Molded Lid with Wave Configured Central Portion", filed May 2, 1996, now U.S. Pat. No. 5,785,201, issued Jul. 28, 1998.
Plastic drum, lid, and ring clamp systems of design permitting reuse now are the subject of substantial interest on the part of industries where avoidance of product contamination is of paramount importance. For example, relatively large drums are used in the food processing industry for intra-company transportation from growing regions to packing centers. These drums, which have lid diameters of about 24 inches, may weigh when loaded, about 600 pounds. Typically, the loaded drums are locally maneuvered by drum handling mechanisms having relatively small gripping devices which attach to a small region of the drum-lid-ring clamp interface and then elevate the drum above the surface for movement. Thus, an applied twisting moment at that small region may induce lid failure. Also, when attaching the popular polymeric two-piece clamp, the somewhat loose, preclamping mode configuration of the two-piece ring clamp may separate in the course of positioning the clamp about the lid and drum. This calls for reassembly of the clamp which, while remaining a simple procedure, often evokes frustration on the part of personnel, particularly those who are inexperienced with the process for attaching the ring clamp.
Drop testing of these all plastic drum-lid-ring clamp systems also has revealed a similar mode of failure wherein the ring clamp and lid rim structures tend to twist upwardly in failure, a phenomenon sometimes referred to by testing personnel as "peeling".